In a medium heavy-bottomed saucepan set over medium-high heat, combine the milk, water, butter, sugar, and salt together. Cook, stirring, until the butter melts and the mixture starts to boil.
½ cup milk, ½ cup water, ½ cup unsalted butter, 1 tablespoon granulated sugar, ½ teaspoon kosher salt
Remove the saucepan from the heat. Add all of the flour to the butter mixture at once, and mix until well combined.
1¼ cups all-purpose flour
Return the saucepan to the stovetop and cook for 2-3 minutes over medium-high heat, stirring vigorously the entire time. The mixture will form a ball and begin to pull away from the side of the saucepan.
Remove the saucepan from the heat and transfer the dough to the bowl of a stand mixer fitted with a paddle attachment (or a large mixing bowl if using a handheld mixer). Set aside for 15 minutes to cool.
Once the dough has cooled, turn the mixer to medium speed and add the eggs. Beat on medium speed until the eggs have been fully incorporated. Add the egg white and beat again until fully incorporated.
3 large eggs, 1 egg white
Tightly cover the bowl with plastic wrap and refrigerate for 10 minutes.
While the dough chills, cut out 15 3x3-inch squares of parchment paper. Set aside.
Fill a Dutch oven with about 3-4 inches of oil. Heat to 350-370°F.
Vegetable Oil
Remove the dough from the refrigerator and transfer it into a pastry bag fitted with a large star tip. Hold the pastry bag vertically over one of the parchment squares and pipe an even circle of dough, just making the ends meet. Repeat until all dough is piped.
Fry the crullers in batches of 3-4 at a time. Gently place a cruller, along with the parchment paper square, onto a slotted spoon. Lower it into the hot oil. Cook for 1 minute, flip the cruller over, and use tongs to remove the paper. Fry for approximately 6 minutes, turning to ensure even cooking, until golden brown.
Remove the crullers from the oil and place on a wire rack to let any excess oil drip off. Let the crullers cool before glazing.
Once the crullers are cool, make the glaze. Heat the chocolate and butter in a microwave-safe bowl for about 40-60 seconds, or until the mixture is smooth. Stir the sifted powdered sugar into the melted butter and chocolate, adding small amounts of hot water until the glaze is thinned as desired.
1 ounce semisweet chocolate, 1 tablespoon unsalted butter, 1-2 teaspoons hot water, ½ cup powdered sugar
Working 1 cruller at a time, dunk the cruller into the glaze, allow any additional glaze to drip off, and place onto a wire rack. Top with sprinkles, serve, and enjoy!
½ cup rainbow sprinkles